Process for preparing composite silvercadmium oxide alloy contact with silver-cadmium surface

ABSTRACT

A COMPOSITE ELECTRIC CONTACT COMPRISING A SILVERCADMIUM OXIDE ALLOY AS THE CONTACT MATERIAL OR ELEMENT AND HAVING A SILVER-CADMIUM LAYER INTEGRALLY FORMED ON THE FACE OPPOSITE TO THE CONTACT FACE IS PREPARED BY APPLYING AN ANTI-OXIDANT LAYER TO THE CONTACT-FORMING FACE, OXIDIZING THE CONTACT MATERIAL WITH AN OXIDIZING ATMOSPHERE, THEN REDUCING THE OXIDIZED FACE TO FORM AN INTEGRAL SILVER-CADMIUM LAYER ON THE FACE OPPOSITE SAID CONTACTFORMING FACE AND THEN REMOVING THE ANTI-OXIDANT LAYER.

June 4, 1974 AKIRA SHIBATA 3,314,640

' PROCESS FOR PREPARAING COMPOSITE SILVER-CADIIUM OXIDE.

ALLOY CONTACT WITH SILVER-CADMIUM SURFACE Original Filed Feb. 8, 1971Wmmwwww wwwummmmw muw'mm "United States Patent Ofice 3,814,640 PatentedJune 4, 1974 3,814,640 PROCESS FOR PREPARING COMPOSITE SILVER- CADMIUMOXIDE ALLOY CONTACT WITH SILVER-CADMIUM SURFACE Akira Shibata, Tokyo,Japan, assignor to Chugai Electric Industrial Co., Ltd., Tokyo, JapanOriginal application Feb. 8, 1971, Ser. No. 113,541, now Patent No.3,688,067. Divided and this application Apr. 10, 1972, Ser. No. 242,859

Int. Cl. C23f 7/02; H01]: N02

US. Cl. 148-63 2 Claims ABSTRACT OF THE DISCLOSURE A composite electriccontact comprising a silvercadmium oxide alloy as the contact materialor element and having a silver-cadmium layer integrally formed on theface opposite to the contact face is prepared by applying ananti-oxidant layer to the contact-forming face, oxidizing the contactmaterial with an oxidizing atmosphere, then reducing the oxidized faceto form an integral silver-cadmium layer on the face opposite saidcontactforming face and then removing the anti-oxidant layer.

This is a division of application Ser. No. 113,541, filed Feb. 8, 1971,now Pat. No. 3,688,067.

This invention relates to a novel electric contact and a process ofproducing the same, and more particularly, to a novel electric contactemploying a silver-cadmium oxide alloy as a contact material and havinga silvercadmium layer integrally formed on the opposite face withrespect to the contact face thereof, and a process of producing saidelectric contact by one-face internal oxidation and reduction.

The conventional processes of producing contact materials ofsilver-cadmium oxide alloy are generally classified into two methods;one is a sintering method by powder metallurgy and the other is a methodof internal oxidation of an alloy. The internal oxidation method is, aswell known, a method of obtaining a contact material of a silver-cadmiumoxide alloy by subjecting a silver-cadmium alloy (cadmium content: 520%by weight) to an oxygen atmosphere at a high temperature to causeoxidation of cadmium and other metals contained in the alloy so that theoxidation proceeds from the circumferential area of the contactmaterial. However a silver-cadmium oxide alloy is diflicult to braze tobrass or Phosphor bronze etc. used as a backing metal or a springmaterial. There are two methods used to solve this problem. One is amethod of applying a silver layer onto the brazing face of a contactmaterial, wherein the silver layer is generally pressure-bonded to asilver-cadmium alloy. According to this method, oxidation progressestowards the inside from the circumference, and due to the way theoxidation of a silvercadmium type alloy progresses, a thin oxide layeris present in the central portion around the midst of its sectionalarea. Such contact material may often show some serious defects such asincrease of wear and decrease of weldability, when practically used, aswear of the contact develops from the contact face into the area of saidthin oxide layer.

Another method to solve the problem in brazing is what is generallycalled a one-face oxidation method, wherein one face of a contact,namely the brazing face, is left unoxidized. In order to leave someportion unoxidized, the fact that oxidation proceeds from thecircumference towards the inside of the material is taken advantage of;that is, two pieces of the contact material mated with each other beforeoxidation may be welded at their mated faces, followed by oxidation fora given period of time so as to leave one face of the contact materialunoxidized. It is, however, almost impossible practically at the presentstage to weld miniature contacts one by one, so usually two sheets of acontact material of a silver-cadmium alloy are mated and welded prior tooxidation, and they are separated in sheets again at the welded facesafter oxidazation. Then each sheet is cut to a given size. In thismethod, however, as the mated faces of the two sheets, which serve asbrazing faces in finished contacts, should be left unoxidized, theperiod of oxidation is restricted and a desired thickness of oxidationcan hardly be obtained.

For overcoming the defects of such conventional contacts, there isdescribed in US. Patent Application No. 815,677, now Pat. No. 3,596,030,a composite electric contact element of silver-cadmium oxide alloy and aprocess of producing the same which comprises providing an elementformed of an alloy of silver-cadmium,

one face of which is a contact-forming face; bonding a layer of silverto the face opposite to said contact-form ing face of said element;applying a barrier layer to said contact-forming face to inhibit oxygendiffusion therethrough and into said contact-forming face; subjectingsaid element with said layers thereon to an oxygen atmosphere at anelevated oxygen diffusion temperature whereby to oxidize the cadmium insaid alloy to cadmium oxide as particles distributed from said silverlayer to said barrier layer; and then removing said barrier layer fromsaid contact-forming face; whereby a composite electric contact elementis produced having a contact face on one side and a silver layer on theopposite face, and in which the cadmium oxide particles increase from aminimum at the contact face to a maximum towards the face with thesilver layer.

The composite electric contact obtained according to the above-describedU.S. Patent Application No. 815,- 677 has the advantage of providing aconstantly equal contact resistance over the entire period of its life,since a layer containing a rather coarse distribution of cadmium oxideforms the initial contact face and a large pressure is applied to thecontact face from a base material, and when the contact material isgradually worn away and the pressure applied from the base material tothe contact face is gradually reduced, a layer comprising more thicklydistributed cadmium oxide begins to appear on the surface forming thecontact face. The composite electric contact produced by this method,however, has a disadvantage, namely, that it employs an expensive silvermaterial on the brazing face. It also has an additional defect ofinsutficient strength, because said silver layer is formed by means ofpressure-bending silver to the contact material. It is, therefore, theprimary object of the present invention to provide a novel electriccontact of a silvercadmium oxide alloy and a process of producing thesame which maintains the advantages of the above-described compositeelectric contact, that is, forming a cadmium oxide layer which iscoarsest on the contact face of the contact material and becomesgradually thicker towards the brazing face opposite to said contactface, but is superior in its strength and economic properties to theabovedescribed composite electric contact which uses a silver layer onthe brazing face.

The gist of the present invention lies in a novel electric contact ofsilver-cadmium alloy and a process of producing the same comprising acontact material formed of a silver-cadmium oxide alloy, one face ofwhich is a contact-forming face; applying an anti-oxidant layer to saidcontact-forming face to inhibit oxygen diffusion therethrough and intosaid contact-forming face; subjecting said contact material with saidlayer to an oxygen atmosphere at an elevated oxygen diffusiontemperature thereby tact material of a silver-cadmium oxide alloy. Thebrazing face is the opposite face with'respect to theco'ntact face.

of said electric contact. Such electric contact is remarkedly superiorin strength and economic properties to the above-described compositeelectric contact having a brazing face formed by pressure-bonding ofsilver.

Various further objects, features and advantages of the presentinvention will be apparent from the following detailed description takenin connection with the accompanying drawings in which:

FIG. 1 is a sectional view of a contact material with an anti-oxidantlayer applied thereto according to one embodiment of the presentinvention;

FIG. 2 is a sectional view of the same showing a state of internaloxidation of a contact after being treated;

FIG. 3 is an enalrged sectional view of the contact material as shown inFIG. 2 cut into the shape of a contact and showing the state of internaloxidation thereof;

FIG. 4 is a sectional view of a contact material according to anotherembodiment of the present invention; and

FIG. 5 is a sectional view of a contact material according to stillanother embodiment of the present invention.

In FIGS. 1 to 3, 1 is a piece of a contact material formed of asilver-cadmium alloy. 4 is an anti-oxidant layer of a metal such asnickel, chromium, aluminum, copper, iron, or alloys thereof which canserve as an anti-oxidation layer in an oxidation atmosphere at a hightemperature. The anti-oxidant layer 4 is applied in a thickness oflop-100,0. to one face of the contact material 1. Said anti-oxidantlayer 4 which is used only for preventing oxidation, is not required tobe thicker, but if it is too thin, it cannot serve as anti-oxidant. Theantioxidant layer may be applied by any method such as pressure-bonding,plating and vaporizing. 'The contact material to which an anti-oxidantlayer is applied as shown in FIG. 1 is heated to be oxidized in anoxidation atmosphere such as oxygen or air at a temperature of 600800 C.The heating time varies depending on the temperature and the kind of theoxidation atmosphere used. As the degree of oxidation progresses almostin proportion to the square of time, the oxidizing time can beadequately selected depending on the thickness of the contact materialto be oxidized. After oxidation is attained, the material is taken outof the furnace, and is heated at 500-800" C. in a reducing atmospheresuch as hydrogen, carbon monoxide or ammonia for reducing the previouslyoxidized surface thereby to form an exterior layer of the originalsilver-cadmium alloy which serves as a brazing face of the contactproduct. The heating time for the reduction treatment is selected as toobtain the exterior layer of a silver-cadmium alloy thick enough forbrazing, usually aboutJ/ of the thickness of the finished contact forinstance, when the thickness of the contact is 2 mm., a heating time of2-10 hours is preferable. After the reduction treatment iscomplete thelayer 4 comprising oxide of a metal of nickel, chromium,

aluminium, copper or iron or alloys thereof is removed with pincers, orby a severing orpickling treatment, there by obtaining a contact ofthe'desired shape. FIGS. 2 and 3 show the state of internal oxidation ofthe contact after reduction treatment-and after the shaped being intoanindividual contact. 2 is an oxidized layer and'3 is a silvercadmiumlayer formed by the reduction. As seen in the figures, said contact hasexcellent contact properties, as

the oxidized layer of cadmium is the coarsest on the cono d o of. c dmum. an

; sslge tq,

. plate to obtain a contact of the present invention. The thus obtainedcontact was mounted on an electromagnetic tact fage ie. the face thatlayer, and becomes gradually thicker towards the opposite brazing face,that is, the silver-cadmium layer 3, and moreover, it is superior instrength due to its integrally formed brazing face. Referring to FIG. 4,another embodiment of this invention is illustrated. Two pieces of,

contactmaterial of silver-cadmium alloy 1 and 1a are mated together andwelded at their mated faces Sinto a singleplate, then subjected tooxidation and reduction treatment as described in FIGS. 1' to 3; Aftersaid treatments are completed, said metal composite plate is sepsaid twopieces are adapted to serve as an anti-oxidant for each other.

A still another embodiment'is illustrated referring to FIG. 5. A pieceof a contactrr'haterial 1b of a silver-cadmium alloy twice as thick asthe desired size of a contact is treated similarly as explained in FIGS.1 to 3, and then cut in half, each of which is thencut to a desiredshape of the contact. v

The contacts prepared by the above-idescribed methods have excellentcharacteristics,compared with those produced by the conventionalmethods. In the conventional contact prepared by pressure-bonding ofsilver and oxi-. dizing from the circumference, the particles of theoxide become larger and their distribution becomes more coarse towardsthe central area from the'circumferential area. Considering thephenomenon from the standpoint of hardness, such a contact is .hardaround'the circumferential area and soft around the central area; Incase of oneface, oxidation the contact is hard near the contact face andbecomes softer towards the brazing face. According to the presentinvention on the contrary, the contact is soft near the contact face andbecomes harder towards the brazing face; consequently, it shows a stablecontact resistance from the beginning. Comparing these three kinds ofcontacts from a viewpoint of wear, an extraordinary wear occurs aroundthe central area of the contact prepared by pressure-bonding of silverand oxidizing fromthe circumference. The ;;contact;formed by one-faceoxidation, shows a tendency that the thinner the'contact becomes bywearing, the more rapid the wear occurs. The wear resistance of thepresent invention, however, tends to increase as the thickness of thecontact "decreases by wearing.

In addition, a brazing face is formed as a silver-cadmium layer byreduction integrally with the contact material of a silver-cadmium oxideaccording to the present invention, the strength of the contact isgreatly improved, compared with a contact prepared by applying silver bypressure-bonding for forming a brazing face.

The present invention is further concretely illustrated.

by the following examples.

EXAMPLE 1 surface obtained by said reduction-treatment was 0.3 mm; 1

Adisc of 8 mm. in diameter was punched out from said shearingtester.-These values were" also determined on 'a conventionalsilver-cadmium oxide 'contac'tof 8 mm. in

diameter and 1.5 mm. in thickness prepared byapplying wa jac t e ant xnt.

silver and oxidizing from the circumference under the same conditions asin this invention (hereinafter referred to as Control Sample A) and acontact of the same dimensions prepared by the method of Us. PatentApplication No. 815,677 (hereinafter referred to as Control Sample B)and the results were compared. The lives of the contacts were alsocompared. The results are shown in Table 1.

The same plate of alloy as used in Example 1 was rolled into a plate ofa thickness 1.5 mm., and plated over with chrominum of 0.01 mm. inthickness, then the plate was oxidized at 800 C. under 1 atm. in anoxygen atmosphere for 96 hours; then it was taken out of the furnace,and reduced at 400 C. under 1 atm. in a CO atmosphere for 5 hours. Thethickness of the silvercadmium layer on the surface obtained by the saidreduction treatment was 0.3 mm. A disc of 8 mm. in diameter was punchedout from said plate to obtain a contact of the present invention. Theobtained contact and Control Samples A and B were tested as described inExample 1 and the results are shown in Table 2.

Two plates of a thickness of 1.5 mm., were prepared by rolling the sameplate of alloy as used in Example 1. The thus obtained two plates weremated with each other and welded at the mated faces. The resultant platewas oxidized at 800 C. under 1 atm. in an oxygen atmosphere for 96hours, taken out of the furnace, and reduced at 300 C. under 2 atm. in ahydrogen atmosphere for 4 hours. The thickness of the silver-cadmiumlayer on the surface obtained by said reduction treatment was 0.2 mm.The welded faces were cut and separated to obtain two plates, and fromeach plate a disc of 8 mm. in diameter was punched out to obtain acontact of the present invention. The obtained contact and ControlSamples A and B were tested similarly as in Example 1 and the resultsare shown in Table 3.

6 EXAMPLE 4 The same plate of alloy as used in Example 1 was rolled intoa plate with a thickness of 3 mm., double the size of those used in theprevious examples. The obtained plate was oxidized at 800 C. under 1atm. in an oxygen atmosphere for 96 hours, taken out of the furnace, andreduced at 750 C. under 1 atm. in a CO atmosphere for 2 hours. Thethickness of the silver-cadmium layer on the surface obtained by thesaid reduction treatment was 0.2 mm. The plate was cut in half to obtaintwo plates, and from each plate a disc of 8 mm. in diameter was pushedout to obtain a contact of the present invention. The obtained contactand Control Samples A and B were tested similarly as in Example 1 andthe results are shown in Table 4.

What is claimed is: 1. A process for preparing an electric contact,comprising:

providing a contact material formed of a silver-cadmium alloy whereinone face of said contact material is a contact-forming face; applying tosaid contact-forming face an anti-oxidant layer of a metal selected fromthe group consisting of nickel, chromium, aluminum, copper, iron andalloys thereof, to inhibit oxygen diffusion therethrough into saidcontact material having said anti-oxidant layer thereon in an atmospherecontaining oxygen at a temperature of 600 to 800 C. to eflect internaloxida tion of the cadmium to form cadmium oxide throughout said contactmaterial, with the cadmium oxide being coarsest adjacent thecontact-forming face and being progressively thicker towards itsopposite face; then heating the thus-oxidized contact material havingsaid anti-oxidant layer thereon in a reducing atmosphere of hydrogen,carbon monoxide or ammonia at a temperature of 500 to 800 C. to reducethe cadmium oxide to cadmium in a zone extending from the exposedsurface of said contact material partway through said contact materialto obtain an integral silver-cadmium alloy exterior surface layer ofselected depth on the exposed surface of said contact material; thenremoving said anti-oxidant layer from the contact material and obtainingan electric contact from said contact material.

2. A process according to claim 1, in which the thickness of saidanti-oxidant layer is from 10 to 100 References Cited UNITED STATESPATENTS 3,596,030 7/ 1971 Shibata 200-166 C 3,607,244 9/1971 Kabayama200-166 C X 3,688,067 8/ 1972 Shibata 200166 C RALPH S. KENDALL, PrimaryExaminer US. Cl. X.R.

. UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION June 4, 1974Patent No 3 1 Dated Inventor(s) Akira Shibata It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as'shown below:

Col. 6, line 35; change "contact material" to --contact forming face;heating said contact material.

Signed and sealed this 17th day of September 1974,

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM po-mso (10-69) USCOMWDC 6o376 p69 U.S. QOVERNMENT PRINTINGOFFICE: @959 O3S6-3344

